Reactance tube



March 13, 1945. M. G. CROSBY REACTANCE TUBE Filed Oct. 21, 1941 2 Sheets-Sheet 1 mOCMEPW [Early 6: 0304 33 A'TTORNEY March 1945- M. G. CROSBY 2,371,285

REACTANCE TUBE Filed 001;. 21, 1941 2 Sheets-Shet 2 INVENTOR G; Crawly ATII'ORNEY Patented Mar. 13, 1945 PATENT OFFICE.

2,371,285 REACTANCE TUBE Murray G. Crosby, Itiverliead, N. Y.. aslignor to Radio Corporation of America, a corporation of Delaware Application October 21, 1941, Serial No. 415,887

9 Claims. (cum-ms) This application concerns a new and improved reactance tube arrangement wherein the feedback voltage isshifted in phase and fed to a control grid by new and improved means. The reactive effect provided by the tube is varied in a novel manner by varying the phase or amplitude of the feedback'voltage.

Reactance tubes of the nature involved here are known in the art. However, as far as appli- --a vector diagram and a simplified phase shifter used in explaining the operation of the phase shifter when it is excited by way of the resistor R.

Figs. 2 and 3 illustrate modifications of the arrangement of Fig. 1. Fig. 3a is a modification of the arrangements of Figs. 2 and 3. Fig. 4 illustrates the feedback voltage phase shifter circuit of Fig. 1 when the resistance R is omitted or of small value. This basic circuit of Fig. 4 also illustrates in principle the feedback phase shifter circuit of Figs. 2, 3, and 311.. Fig. 5 is a vector diagram used in' illustrating the manner in which the feedback voltage is shifted by the fundamental circuitof Fig. 4.

In Fig. 1, tube 2 is the reactance tube which is caused to display a variable reactance between leads 4. The leads 4 are connected between the anode 6 and cathode ii of tube 2. Alternatin voltage from any source is fed to. the anode 6,

say, for example, by way of leads 4 and blocking condenser 6, and thence by way of blocking condenser lll, resistance R, and inductance l2 to the controlling grid electrode ll. The inductance I2,

in combination with variable resistance i6, provides the feedback phase shifting circuit. The screening electrode 18 and suppressor grid electrode 20 may be connected, as shown, to positive and negative points I and 9 respectively on a source or sources .of potential not shown. The plate 6 may be'co ected by an inductance RFC to a positive point 6 one. source of potential.

Bias for the tube is-supplied by a resistor and condenser arrangement 22. The resistance i6 maybe replaced by a tube impedance or similar means which may be readily modulated. as illustrated in Fig. 3. which is described in detail hereinafter.

The resistance R serves to isolate the phase shifter circuit from the circuit to which the reactive eflect is applied.' It also serves to attenuate the feedback so that too much feedback will not be obtained and the circuit will not oscillate. with this circuit I have found that the phase may be shifted exactly 90 degrees and may be adjusted by varying resistanceJO. The circuit including resistance R, inductance l2 and resistance I6 shifts the voltage supplied from the anode 6 to the controlling electrode II. The manner in which this shiftis accomplished has been illustrated in Figs. 1A and 1B. In Fig. 1B; the inductance I2 is shown as having two sections and the phase shifter is shown as having an input between points D and C (see corresponding points in Fig. 1) and output points B and C. Fig. 1A shows the vector diagram for the phase shifter circuit which is redrawn in Fig. 1B. The voltage fed to the phase shifter from plate 6 is E. R is made large compared to the reactance ,of-Xl so that the current will be largely determined by the resistance, but due to the inductive reactance of XI, the phase of the current will be slightly lagging as shown by vector I. The voltage drop across Xi will lead the current as shown 'by vector XII. The voltage drop across X2 will be opposite in phase to XII as shown by vector X2I. The voltage drop across RI (l6) will be in phase with the current as shown by R11.

lagging in phase with respect to E, the reactive effect is that of a shunt inductance because a lasging current is caused to flow in the plate circuit of the reactance tube.

When R is omitted or has a negligible value,-

the phase shifter input is considered to be at AC, as illustrated in Fig. 4. The phase shifter shifts the phase of voltage El, that is, of the voltage supplied between the anode 6 and ground C by way of cathode 6, etc., by an amount depending upon the magnitude of the reactance of LI and L2 and the resistance Ri of i6. The vector diagram of this type of phase shifter is shown in is Fig. 5. El causes a current to flow through Li relation may be exactly obtained. Since E2 is In and RI so that a reactance drop XLII will appear across points to A of Fig. 4, and a resistance drop RII will appear across terminals 0 to C of Fig. 4. A reactance drop XmI will appear across the terminals 0 to B of Fig. 4 by virtue of the inductive coupling'between, LI and L2. Voltage El is the resultant of the reactance and resistance drops XLI I and RII. The output voltage of the phase shifter E2 is a resultant of the mutual reactance drop XmI and the resistance drop RII. It can be seen that El differs from E2 in phase by an amount 0, depending upon the relative valuesef the resistance voltage drop R11 and the reactive voltage drops XLII and XmI. Consequently, by varying the value of RI the phase may be varied between zero and almost 180 degrees.

From the vector diagram of Fig. 5, it can be seen that as the resistance RI of i6 is varied relative to, say, a value at which the voltage E2 fed across the grid l4 and cathode 5 is substantially in phase quadrature with respect to the voltage El, the value of the reactive effect supplied by the leads, 4 is varied. The resistance It may be modulated in accordance with signals to thereby modulate the reactive effect appearing across leads 4 in accordance with signals. Moreover, it can be seen that as BI is varied between zero and a value equal to the reactive impedance, the phase s t, 0, will be varied, but the amplitude of the output voltage E2 will not vary since E2 is always equal to El. Consequently there will be little or no amplitude modulation of the voltages fed back to the grid l4, and as a consequence, when the reactants tube is used for modulating the wave length of wave energy, the same is accomplished with little or no amplitude modulation thereof. I

In the circuit of Fig. 3, the efl'ective reactance of the tube is varied by varying the phase of the feedback When the feedback is 90 degrees, the tube acts as a pure reactance. When the phase is zero degrees, the tube acts like a low resistance. For the phase positions between zero and 90 degrees, the reactive eifect is that of a reactance and a resistance. Hence, for some intermediate positions, the reactive componentis smaller than it was at 90 degrees and the resistance compo nent is increased. Thus, if the phase of the feedback is varied either side, for instance, of 45 degrees leading, the reactive eilect varies from a condenser with a resistance in shunt, towards a larger condenser with a higher resistance in shunt or towards a smaller condenser with a small resistance in shunt. The result is a variation of the reactive effect of the tube which may be used to produce phase or frequency modulation, or for automatic frequency control. The variable resistance component will have a tendency to vary the amplitude of energy in the circuit to be controlled, but this may be eliminated by subsequent limiting or by making the range of operation small so that the effect may be neglected.

For the circuits of Figs. 1 and 3, the phase is lagging so that the tubes have an inductive reactive eflect. In Fig. 3 the eil'ect would be modulated from an inductance with a resistance in shunt, towards a lower inductance with a higher resistance in shunt (when the phase is shifted towards 90 degrees by modulating the plate resistance of tube 40 to a low value), or towards a higher inductance with a lower resistance in shunt (when the phase is shifted towards zero degrees by modulating the plate resistance of tube 40 to a higher value) While the preferred arrangements of Figs. 1, 2, 3. and 3a use a rather large value of the resistance R, this is not an absolutely necessary requirement. In the absence of this resistor, or when the resistor is low in value. the phase shifter consisting of inductance l2 and resistance It is still capable of producingthe required 90 degrees phase shift. However, the resistor has an isolating function which prevents the phase shifter circuit from loading the circuit which is controlled and also has an attenuating function which prevents the degree of feedback from being sogreat as to cause instability. The manner in which the phase shifter operateswithout the series resistor is shown in Figs. 4 and 5.

If desired, however, the resistance 16 may be adiusted to provide substantially a phase quadrature relation between the voltages El and E2 so that the voltage fed back to the grid I4 is substantially in phase quadrature with respect to the voltage on anode 6. The reactive effect between leads 4 may then be varied by varying the potential on one of the electrodes of the tube as illustrated in Fig. 2. This may be accomplished by' connecting a modulation source 30 in series between the electrodes I4, I 8 or 20 and an appropriate source of potential. This may be arranged in any desired manner as, for example, switches SI and S2 may connect a selected point, 3, l or 9, through the modulation source to 3', I or 9' at wlliiiegh the required electrode potential is sup- P In the modification of Fig. 3, the resistance I6 is replaced by the impedance between the anode 3i and cathode." of tube 40. This phase shifter of Fig. 3 is in principle the same as the phase shifter of Fi 1, and the manner in which the voltage between points D and C or A and C is shifted to supply an output voltage between points B and C has been illustrated in Figs. 1A and 1B and in Figs. 4 and 5.

The reactive effect appearing between leads 4 may be modulated in accordance with potentials of any nature by applying the same between the grid 42 and cathode 38 of tube 40. The variation of the plate impedance of tube 40 causes a variation of the phase of the voltage fed from the anode i to the control electrode I 4. This variation of phase varies the reactance appearing between leads 4; hence, modulating potential or automatic frequency control energy may be applied to the grid 42 and cathode 38 of the tube 4| to produce a variablereactive effect between leads 4 which may be used for frequency modulating, phase modulating, or automatic timing.

With this type of reactive tube a combination of the variation of the phase of the feedback voltage and a modulation of a reactance tube element voltage may be effected to provideza certain desired characteristic of reactance variation.

For example, as illustrated in Fig. 3a. the modulating or control potentials may be applied between the grid 42 and cathode 38 and also between the grid l4 and cathode of tube 2. When tube 40 is biased negative the plate impedance of tube 4! increases so that resistance RI of the is changed from a low inductance towards a higher one. Consequently the phase of modulating potentials must be opposite in order for the reactive efiects to be cumulative. This opposite phase adjustment is efiected by throwing switch S to point X. If the unmodulated phase position is 135 degrees lagging, the effect of a negative bias shift on tube 40 will be to increase the effective inductance of the reactance tube. For this condition the in-phase connection of the modulating potentials (adjusted by throwing switch S to point Y) is required.

What is claimed is:

1. In a variable reactance, an electron discharge tube having an anode, a cathode and a control grid, means for impressing an alternating current voltage on said anode and cathode, an inductance in a series circuit between said anode and control grid, and an adjustable impedance connecting a point intermediate the terminals of said inductance to the cathode of said tube whereby a variable reactive effect may be produced between the anode and cathode of said tube by varying said adjustable impedance, thereby varying the phase of the voltage fed back to said control grid.

2. In a variable reactance, an electron discharge device having an anode, a cathode and a control grid, means for impressing alternating voltage between said anode and cathode, a resistance and an inductance in series between said anode and control grid, an adjustable resistance connecting a point intermediate the terminals of said inductance to said cathode whereby a voltage the phase of which may be adjusted is applied from said anode to said control grid and a reactive effect is set up between said anode and cathode, and means for controlling the gain of said tube to thereby control the size of said reactive effect.

3. In a tube reactance,'an electron discharge tube having an electron receiving electrode, an electron. flow control electrode and an electron flow producing electrode, means for applying an alternating voltage to said electron receiving electrode, means for applying a voltage from said electron receiving electrode to said electron flow control electrode, and means for varying the phase of said last named applied voltage and the gain of said tubein accordance with control potentials to thereby correspondingly vary the reactance provided between the electron flow producing electrode and electron receiving electrode.

4. An electron discharge device having, an electrode serving as an anode, a control grid and a cathode, means for impressing alternating current voltage on said electrode serving as said anode and said cathode, a resistance and an inductance in series between said electrode serving as said anode and said control grid, an adjustable impedance connecting a point on said inductance to the cathode of said tube, whereby the voltage fed back from said electrode serving as an anode to said control grid may be shifted in phase an amount sufilcient to produce a reactive effect between said electrode serving as an anode and said cathode, and means for varying the value of said reactive effect including means for varying the value of said impedance and for varying the gain of said tube.

5. In a. variable reactance, an electron discharge tube having an anode, a cathode and a control electrode, connections for impressing an alternating current voltage on said anode and cathode, an inductance in a series circuit between said anode and control electrode, an adjustable resistance connecting a point intermediate the terminals of said inductance to the cathode of said tube whereby a reactive effect is produced between the anode and cathode of said tube, and connections for varying said adjustable resistance to thereby vary the said reactive efiect.

6. In a signalling system of the class described, an electron discharge device having an anode, a cathode and a control grid, connections for applying alternating current across the anode and cathode of said device, a resistance and an inductance in series between the anode and control grid of said device, an electron discharge tube having an anode, a control electrode and a cathode, a connection including the impedance in said tube between its anode and cathode in a lead between a point on said inductance and the cathode of said device and a source of control potentials coupled to the control electrode and cathode of said tube.

7. In a signalling system of the class described, an electron discharge device having an anode, a cathode and a control grid, a source of alternating c urrent coupled across said anode and cathode, a coupling including a series inductance between the anode and control grid of said device, a resistance coupling a, point on said in ductance to the cathode of said device, a'source of modulating potentials and a coupling between said source of modulating potentials and the cathode and another electrode of said device.

8. In apparatus of the class described, an electron discharge device having an anode, a cathode and a control grid, connections for applying alternating current across said anode and cathode, a coupling including a series inductance between the anode and control grid of said device, a tube having an anode and a cathode in a series circuit between a point on said inductance and the cathode of said device, said tube having a control grid, a source of modulating potentials and connections for applying modulating potentials from said source to an electrode in said tube and in said device.

9. In a tube reactance, an electron discharge tube having an electron receiving electrode, an electron flow control electrode and an electron flow producing electrode, means forapplying alternating voltage to said electron receiving elec- .trode, means for applying alternating voltage of the same frequency to said electron flow control electrode, and means for relatively varying the phases of said applied voltages and the gain of said tube in accordance with signals to thereby correspondingly vary the reactance provided be tween the electron flow producing electrode and electron receiving electrode.

MURRAY G. CROSBY. 

